The present invention relates to an improvement of apparatus for producing single crystals, which apparatus is for producing various crystal materials of semiconductors, dielectric material, magnetic material and the like by the Czochralski method.
For the production of single crystal materials such as semiconductor silicon single crystals, methods for obtaining them as rod-shaped single crystals by the Czochralski method (referred to as xe2x80x9cCZ methodxe2x80x9d hereinafter) have been widely used so far.
Apparatuses for producing single crystals used for this CZ method usually comprise a crucible for accommodating a raw material melt disposed in a chamber, a support shaft for supporting the crucible, a pulling mechanism for pulling a crystal from the melt, a rotation mechanism for rotating the crucible, and a transfer mechanism for vertically moving the crucible, as well as members in a furnace such as heaters and heat insulating materials disposed in the chamber, so that a single crystal can be produced.
It has been widely known that, when crystal growth is attained by this CZ method, ingredients of the crucible such as quartz crucible for accommodating the raw material for the crystal growth, for example, oxygen, are immixed into the resulting crystals, in addition to those ingredients originally contained in the raw material.
The amount of the impurities to be immixed in the crystal may vary depending on the rotation number of the pulled crystal, the rotation number of the crucible, temperature distribution of the raw material melt and the like. That is, the crystal rotation number affects the convection in the melt, the crucible rotation number affects the oxygen concentration itself in the melt, and the temperature distribution in the raw material melt affects the convection in the melt.
Moreover, since depth of the melt in the crucible gradually decreases as the crystal grows, it must be devised that the melt surface should be controlled to position at a fixed position in order to control the diameter of the growing crystal, and it is necessary to move the crucible upward to secure constant relative locational relationship between the melt and the heaters as the crystal grows. Therefore, many of conventional apparatuses for producing crystals based on the CZ method have been provided with functions for rotating a crucible-supporting shaft as well as vertically moving the crucible. In particular, a rotation-driving unit for the crucible-supporting shaft must also be vertically moved with the crucible-supporting shaft. As shown in FIG. 4, in a conventional apparatus for producing single crystals, for example, the crucible rotation driving unit 26 has been provided on a slider 31 of the mechanism 30 for vertically moving the crucible, which vertically moves with the crucible-supporting shaft 4.
In such a conventional apparatus as mentioned above, the melt surface may be vibrated. Such vibration of the melt surface may leads to disadvantages, that is, the growing single crystal may become a polycrystal, or even it becomes impossible to continue the crystal growth when the situation gets worse. Therefore, the cause for the vibration was investigated, and it has been revealed that vibration of the crucible-supporting shaft constitutes its major cause. That is, vibration is generated by rotation of an electric motor, which is the driving power source for the crucible rotation, this vibration in turn vibrates the mechanism for vertical movement, and this vibration is transmitted to the melt via the crucible-supporting shaft and the crucible.
The present invention has been accomplished in view of such problems, and its object is to provide means for absorbing and eliminating the vibration generated by the crucible rotation driving unit, or preventing transmission of the vibration to the melt, or attenuating the vibration.
In order to achieve the aforementioned object, the 1st embodiment of the invention relates to an apparatus for producing single crystals by the Czochralski method, the apparatus comprising at least a support shaft for supporting a crucible for accommodating a raw material melt, a pulling mechanism for pulling a crystal from the melt, a rotation mechanism for rotating the crucible, and a transfer mechanism for vertically moving the crucible, wherein a crucible rotation driving unit constituting the rotation mechanism for the crucible is fixedly installed on a substructure of the apparatus for producing single crystals.
When the crucible rotation driving unit consisting of an electric motor and means for speed change and reduction is fixedly installed on the substructure of the apparatus for producing single crystals as defined above, vibration generated by the electric motor constituting the crucible rotation driving unit is absorbed by a fixed end, i.e., the rigid substructure, and attenuated. Thus, the vibration is not substantially transmitted to the melt surface via the crucible-supporting shaft and the crucible. Therefore, the vibration of the melt surface, which may be a cause for generating dislocations in growing single crystal ingots, can be substantially eliminated.
In this case, the term xe2x80x9csubstructurexe2x80x9d of the apparatus for producing single crystals means frames, concrete substructures, substructures of working houses and the like for supporting the apparatus for producing single crystals. It may be any means that can fix the crucible rotation driving unit without being vibrated by the unit, and it is not limited by a literal meaning of the word.
The 2nd embodiment of the invention relates to an apparatus for producing single crystals by the Czochralski method, the apparatus comprising at least a support shaft for supporting a crucible for accommodating a raw material melt, a pulling mechanism for pulling a crystal from the melt, a rotation mechanism for rotating the crucible, and a transfer mechanism for vertically moving the crucible, wherein, in the rotation mechanism for the crucible, a ball spline is used for power transmission between a crucible-supporting shaft and a crucible rotation driving unit, and the crucible rotation driving unit is fixedly installed on a substructure of the apparatus for producing single crystals.
When the crucible rotation driving unit consisting of an electric motor and means for speed change and reduction is fixedly installed on the substructure of the apparatus for producing single crystals, and a ball spline is used for power transmission between the crucible-supporting shaft and the crucible rotation driving unit in the rotation mechanism for the crucible as defined above, only vibration attenuated by being absorbed into the substructure is transmitted to the ball spline, and therefore the vibration of the melt surface is substantially eliminated without affecting at all the function of the ball spline for transmitting rotation simultaneously with the vertical movement. Thus, single crystals can be produced safely and efficiently.
In the 3rd embodiment of the invention, a rubber-like elastic belt and a pulley, or a rubber-like elastic timing belt and a timing pulley are used as means for transmitting rotation between the crucible-supporting shaft and a ball spline shaft, and between a ball spline sleeve and an output shaft of the crucible rotation driving unit.
By using a rubber-like elastomer as a material for transmitting rotation between the shafts as defined above, the vibration generated by the crucible rotation driving unit is attenuated and absorbed by rubber-like elastic deformation, and vibration transmitted to the melt surface is substantially eliminated. Therefore, the cause etc. for generating dislocations in growing crystals is eliminated, and crystals can be produced safely and efficiently.
The 4th embodiment of the invention relates to an apparatus for producing single crystals by the Czochralski method, the apparatus comprising at least a crucible-supporting shaft for supporting a crucible for accommodating a raw material melt, a rotation mechanism for rotating the crucible, and a transfer mechanism for vertically moving the crucible, wherein vibration at the upper end of the crucible-supporting shaft for supporting the crucible is controlled to be 100 xcexcm or less along a direction perpendicular to the shaft.
In an apparatus for producing single crystals by the Czochralski method, if the vibration at the upper end of the crucible supporting shaft for supporting the crucible is 100 xcexcm or less along a direction perpendicular to the shaft, vibration of the crucible-supporting shaft directly acting on the whole raw material melt becomes small, and thus the vibration of the raw material melt surface, which is the cause for generating dislocations in growing crystals, can be substantially eliminated.
The expression of xe2x80x9cvibration of 100 xcexcm or lessxe2x80x9d used for the present invention, for example, means that a rocking range of an object shaken by the vibration is 100 xcexcm or less, and does not mean that the amplitude of the vibration (half of the rocking range of the shaken object) is 100 xcexcm or less.
In the above apparatus, as the 5th embodiment, the transfer mechanism is preferably provided with a slider that vertically moves with the crucible-supporting shaft, and vibration of the slider along a direction vertical to the crucible-supporting shaft is preferably controlled to be 200 xcexcm or less.
When the vibration of the slider is 200 xcexcm or less, the vibration of the crucible-supporting shaft can be 100 xcexcm or less. Thus, the vibration of the raw material melt surface, which is the cause for generating dislocations in growing crystals, can be substantially eliminated.
Further, in the above apparatus, as the 6th embodiment, vibration generated by the crucible rotation driving unit, which is a power source for the rotation mechanism, is preferably controlled to be 50 xcexcm or less.
If the vibration generated by the crucible rotation driving unit is 50 xcexcm or less as defined above, amplification of the vibration by the crucible transfer mechanism can be prevented, and thus the vibration of the raw material melt surface, which is the cause for generating dislocations or the like in growing crystals, can be substantially eliminated.
Further, as the 7th embodiment of the invention, if single crystals are produced by using the apparatus for producing single crystals according to any one of 1st-6th embodiments, the single crystals can be stably produced without generating dislocations and the like in the single crystals because the vibration of the raw material melt is substantially eliminated.
The 8th embodiment of the invention relates to a method for producing single crystals based on the Czochralski method by supporting a crucible accommodating a raw material melt by a crucible-supporting shaft, and rotating and vertically moving the crucible, wherein the single crystals are produced while vibration at the upper end of the crucible-supporting shaft is controlled to be 100 xcexcm or less along a direction perpendicular to the shaft.
If single crystals are produced while the vibration at the upper end of the crucible-supporting shaft is controlled to be 100 xcexcm or less along a direction perpendicular to the shaft, the generation of dislocations and the like in single crystals caused by vibration of the raw material melt can be prevented, and thus the production efficiency of single crystals can be improved.
In the conventional mechanisms for rotating crucible, vibration of the crucible-supporting shaft is transmitted to the melt surface, and it constitutes the cause for generating dislocations and the like in the growing single crystals. In contrast, according to the present invention, by fixing the crucible rotation driving unit on the substructure of the apparatus for producing single crystals, and by using a ball spline and, for example, a timing belt for transmission of rotation, the vibration is absorbed and attenuated, and thus the vibration of the melt surface is substantially eliminated. Therefore, thanks to the elimination of the cause for generating dislocations in growing crystals, single crystals can be produced safely and efficiently.